In the known embodiments of these types of thermostatic mixer devices, said mixing member located inside the envelope forms a member separated from the envelope shaped as a skirt. As a consequence it is needed to separately manufacture these two members and to assemble the same before they are connected to the other component parts of the mixer device. Therefore, this structure involves complications in manufacturing and assembling the device, which have a negative influence both on the manufacturing costs and on the organization of the production.